Synergistic optimization of thermoelectric properties and structural stability in Cu2Se thin films via Bi-induced resonant levels

Copper selenide (Cu 2 Se) thermoelectric materials offer attractive thermoelectric properties, environmental friendliness, and abundant raw materials, making it a promising candidate for self-powered flexible thermoelectric thin film devices. Nevertheless, its intrinsically high carrier concentration and complex microstructural defects hinder further performance enhancement in flexible films. In this study, magnetron sputtering was employed to in situ deposit Cu 2 Se flexible thin films, with co-sputtering of bismuth (Bi) cations implemented to modulate the films’ microstructure and carrier concentration. Theoretical analyses revealed that Bi doping induces the formation of resonance levels, orbital hybridization, and phase transitions, introducing a pronounced change in the density of states proximate to the Fermi level can substantially augment the Seebeck coefficient, while synergistically modulating the carrier effective mass and mobility, thereby optimizing the band structure and electrons and phonons transport properties of Cu 2 Se thin films. Experimental results demonstrated that the doped sample (Cu 1.94 Bi 0.06 Se)(Cu) 0.59 with annealing achieves a power factor of 5.92 μW cm −1 K −2 at 573 K, representing an approximately 150% enhancement over the undoped sample. This investigation confirms that cation doping combined with appropriate thermal treatment effectively mitigates structural defects arising from compositional deficiencies, such as copper vacancies, and enhance its structural stability. By regulating the microstructure and band structure, structural stability and carrier concentration can be optimized, thereby significantly improving the thermoelectric properties of Cu 2 Se flexible films. This research provides a foundational framework for flexible thin film thermoelectric devices based on high-performance Cu 2 Se.